This invention relates to a method and apparatus for joining components by drawn arc welding.
Drawn arc welding is widely used to join components in many industries, including the manufacture of automotive vehicles, components of automotive vehicles, and appliances, and is also used in the construction of ships. In drawn arc welding, the components to be welded are brought into contact with one another and each component is connected to the welding voltage supply so that a current is drawn through the components. One of the components is lifted away from the other component to define a gap (the size of the gap is typically of the order of millimeters or a fraction of a millimeter) while maintaining the current through the components. Accordingly, an arc is drawn through the gap and extends between the components, melting or softening a portion of them. The current is then turned off, and the components are allowed to move back into contact, where they are welded together by the molten metal. The parts may be pressed together to improve weld quality. Drawn arc welding requires relatively simple or xe2x80x9cleanxe2x80x9d equipment as compared to other welding processes.
However, drawn arc welding has heretofore been limited to welding relative small studs (typically 0.25 in. or less in diameter) and similar sized brackets. The welding of tubular brackets and large studs has not been possible, because it was not possible using prior art drawn arc welding techniques to assure a consistent weld around tubular members and large studs. In many applications, a consistent weld is critical, because welds that have voids or gaps are not sufficiently strong.
According to the present invention, a magnetic field is generated by energizing electromagnetic coils to generate a magnetic field acting through said gap transversely with respect to the arc. Accordingly a resultant force is generated (as determined by the three finger rule well known to those skilled in the art) which impels the magnetic force along the gap. In the case of tubular brackets, the arc is impelled circumferentially around the bracket, so a consistent weld may be obtained around the circumference of the bracket. The field may be varied by known techniques, such as using additional coils placed appropriately or by physically moving the coils, to drive the arc between the inner and outer diameters of the component. Because of the impelled arc, brackets and nuts may be welded using the drawn arc welding technique that are significantly larger than is possible using prior art techniques, and tubular brackets may be welded using drawn arc techniques than could not be welded by drawn arc welding techniques known in the prior art.
It is important that the magnetic field be generated substantially transverse to the arc. It has already been proposed, for example, in U.S. Pat. No. 4,531,042, to generate a magnetic field acting parallel to the arc. However, this field will only contain the arc, and will not impel the arc relative to the components being welded.